1. Field of the Invention
The present invention relates to a screen printing machine, and more particularly, to a screen printing machine which screen-prints applying material such as a cream solder or a conductive paste on a substrate such as a printed wiring board (PWB) or a printed circuit board (PCB) as a pretreatment for mounting an electronic component to the substrate.
2. Description of the Related Art
For example, as disclosed in Japanese Patent Application Laid-open No. 2008-105294 (hereinafter, “Patent Document 1”), a screen printing machine includes a screen mask in which a print pattern is formed, and a squeegee. The screen mask is mounted to a predetermined mask mounting area. In a printing process, the squeegee moves over the screen mask relative to the screen mask. Applying material supplied to the screen mask is rolled by the squeegee and applied to a substrate through a print pattern. The print pattern of a screen mask corresponds to each substrate. Therefore, when a substrate that is a production object is changed, a screen mask is also changed. Conventionally, as expressively described in Patent Document 1, a change of screen masks necessitates replacement of squeegees.
Conventionally, replacement work of a screen mask required attaching and detaching a squeegee even when changing the squeegee was not required. In other words, applying material is adhered to a squeegee immediately after use. Therefore, a state exists where the applying material adhered to the squeegee is more likely to drip down into a mask mounting area. On the other hand, a substrate conveying mechanism and a substrate supporting mechanism are facing the mask mounting area. When the applying material drips onto these mechanisms, there is a risk that a substrate may become dirty or operations of the mechanisms may be obstructed. Therefore, conventionally, processes involving replacing a screen mask inevitably require that the squeegee be removed in advance. As a result, preparation work is time-consuming. In addition, the versatility of squeegees cannot be fully utilized.
In addition, letting applying material adhered to a squeegee stand for an extended period of time causes a change in viscosity of the applying material by the time of printing and may result in a decline in quality. Therefore, work for wiping off applying material adhered to the squeegee must be performed at the end of printing.